Sticking unmatched batteries in a charger

What happens if I stick a 2000mAh and a 2500mAh battery side by side in a charger? Will the higher capacity battery charge the lower capacity battery so I get two batteries at 2000mAh or will I get what they're rated, or close to?

Also, the "rated" capacity and actual capacity are often very different. So you might be OK because your 2000mAh and 2500mAh batteries are actually fairly similar batteries that just have different ideas of what the "mAh" part really means. And/or have been worn down differently.